Synchroscope



Jan. 19, 1954 RIGHTS 2,666,900

SYNCHROSCOPE Filed Feb. 21, 1948 WITNESSES: INVENTOR Ma 54 W ATTORNEY atenied Jan. 19, 1954 SYNCHROSCOPE Herbert T. Rights, New Brunswick, N. J assignor to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application February 21, 1948, Serial No. 10,101

This invention relates to synchroscopes and circuits therefor and more particularly to devices for indicating the synchronization of polyphase alternating current systems and rotating machines.

Among the more common types of synchroscopes in present-day use are synchroscopes of the moving iron-vane type and the electrodynamic type. Lamps are also employed as synchronous indicators because of their simplicity but have a relatively high burden and are not sensitive to slight variations in voltage. Syn-- chroscopcs of the instrument type when used on 100 or 120 volt, 60 cycle system, usually consume about three watts. In accordance with the invention it is proposed to provide a synchroscope for polyphase systems which will consume only about 5% of this power, or less, according to the design.

To indicate the synchronization of machines such as the engines of a multi-engined craft for example, tachometers have been employed. Tachometers, however, are not accurate and very frequently fail to indicate the relative speed or" two engines within an accuracy of twenty revolutions per minute. In accordance with the invention, it is also proposed to provide a simple, accurate and low-burden synchroscope for such machines employing polyphase generators. It is, therefore, an object of the invention to provide a novel, improved, reliable, low-burden synchroscope.

It is a further object of the invention to provide a compact device for indicating both syn chronization and synchronized speed and/ or irequency of two polyphase generators.

It is an additional object of the invention to provide a synchroscope system employing .a conventional type of electrical measuring instrument.

It is another object of the invention to provide an improved synchroscope of the multipleinstrument type capable of indicating which of two generators is rotating the faster.

It is another object of the invention to provide an electrical measuring instrument having a permanent magnet structure which is shaped to be positioned in a sector of a circle.

It is a further object of the invention to provide a synchroscope which employs a rectifier and a DArsonval type of instrument.

It is a still further object of the invention to provide a measuring device employing a plurality of electrical measuring instruments having indicators which traverse a common dial.

4 Claims. (01. 324-91) Other objects of the invention will be apparent from the following description taken in conjunction with the accompanying drawing in which:

Figure 1 is a diagrammatic view ofa syn chronous indicating device associated with two three-phase systems.

Fig. 2 is a schematic view showing the arrangement and certain details of an indicating device embodying three electrical measuring instruments.

Fig. 3 is a diagrammatic view or a bridge circuit employed with a direct-current measuringinstrument.

Fig. l is a diagrammatic view of a synchronous indicating device associated with two, threephase generators which are driven by rotating machines to be synchronized, and

Fig. 5 is three views showing the face or" an indicating device and the relative positions of the indicators on a common dial for three different phase relationships between two threephase systems.

Referring to the drawing, Figure 1 shows a three-phase system i which may be connected by means of a circuit breaker ii to a three-phase system 5. System I has phases or terminals A, B and C which correspond to phases or terminals A, B, and C, respectively, of system 5. An indicating device i comprising electrical measuring instruments H, 13 and I5, is connected between systems I and 5. The instruments H, is and 45 may be any conventional alternating current measuring instrument such as an alternating-current voltmeter, or may be a combination or" a rectifier and direct-current electrical measuring instrument as hereinafter more fully described. The instrument H is shown connected between phases or terminals A and A or" the two systems. instrument is is connected between phases or terminals C aand B and instrument is is connected between phases or terminals B and C- It is to be observed that the instrument ii is connected between corresponding phases or terminals of systems I and '5 and that instruments l3 .and are connected between the other diiiering phases or terminals of the systems i and 5.

In the indicating device I the instruments ii, l3 and I5 are positioned equidistant from each other. Each of the instruments Ii, i3 and it has indicators or pointers 2i, 23 and 25, respectively. When the instruments are deenergized, the pointers 2!, 23 and '25 which are in different planes intersect when in zero position at a common point in the center as shown in the drawing.

Referring to Figure 2, an indicating device 31 is shown comprising three permanent-magnet moving-coil instruments 4|, 43 and 45. Since the construction of the instruments 4|, 43 and 45 is identical, we may confine our discussion to the instrument 4| which comprises a magnet-structure 49 and a moving-coil 5 I. The magnet-structure 49 comprises an angular permanent-magnet 53 having legs 55 and 51 which are at an angle of approximately 120 to each other. A pole tip 59 which is preferably formed of soft iron is associated with the leg 55 of the permanent magnet 53. Similarly a pole tip 6| is associated with the leg 51 of the permanent magnet 53. The pole tips 59 and GI have pole salients with arcuate concavities 63 and 65, respectively, facing each other to form a substantially cylindrical opening within which the moving coil 5| may rotate. Each of the pole tips 59 and 61 have arcuate surfaces 91 and 69, respectively, on the side thereof opposite the permanent magnet 53, the arcuate surfaces having a radius approximating the radius of the indicating device 31 in which the magnet structure 49 is positioned. It will be observed that the outline of the magnetstructure 49 is substantially sector-shaped and is designed to occupy almost one third of a circle. It will also be observed that the magnet structures of the instruments 4|, 43 and 45 are spaced apart to minimize the effects of one magnet structure upon another.

Although the instruments 4|, 43 and 45 are identical, it is to be pointed out that the positions of the indicators or pointers for the instruments 4|, 43 and 45 are adjusted so that each pointer rotates in a different plane to avoid contact or interference with any other.

The electrical measuring instrument 4| is provided with an indicator 1| which is associated with the moving coil 5|. In accordance with the usual practice, a helical spring 13 is afiixed between the moving coil 5| and the stationary portion of the electrical measuring instrument 4!, such as its magnet structure 49, to efiect a bias on the moving coil 5| to oppose movement of the indicator 1| in the up-scale or clockwise direction from a zero position wherein the coil is deenergized.

As is well understood in the art, suitable bearing assemblies (not shown) are provided to permit rotation of the moving coil 5| and the indicator 1| when a change in the energization of the instrument takes place.

In Figure 3 a conventional type of bridge rectifier circuit is shown associated with a directcurrent electrical measuring instrument. The leads 9| and 93 may be connected between the conductors of a suitable alternating current source, such as between phases of two threephase systems or two three-phase generators. The lead 9| is shown connected through a resistor 95 to a full-wave bridge-type rectifier 99. The rectifier 99 comprises rectifiers I9I, I03, I95 and I01, which may be of the copper-oxide type, and are positioned in the four legs of the bridge circuit. An electrical measuring instrument of the direct-current type, is connected between terminals III and II3 of the bridge circuit. The lead 93 is connected to a terminal II5 of the bridge circuit and the resistor 95 is connected to a ter minal II1.

As is well-known in the art, when a positive potential is applied to the lead 9|, current flows through the resistor to the terminal II1 through the rectifier IIII to the terminal II3, from the terminal II3 through the direct current instrument I 99 to terminal I I I, from terminal II I through the rectifier I95 to terminal H5, and from terminal II5 to the lead 95.

If, on the other hand, a positive potential is applied to the lead 93, current flows through the lead 93 to the terminal II5, from the terminal I I5 through rectifier I93 to the terminal I I3, from the terminal I I9 through the direct-current electrical measuring instrument we to the terminal III, from the terminal III through the rectifier I91 to the terminal II1, and from terminal II1 through the resistor 95 to the lead 9|.

It is to be observed that in both cases current flows from the terminal H3 through the measuring instrument I99 to terminal I II whether the positive potential is applied to the lead 9| or 93. In other words, a unidirectional current is applied to the instrument I99 irrespective of the direction of the current in the leads 9| and 93 or irrespective of the fact that alternating current is applied to the leads 9| and 93. With an increase in voltage-difference between the leads 9| and 93, the indicator for the measuring instrument moves in the up-scale direction.

Fig. 4. shows a three-phase alternating-current generator I4| which is driven by a rotating device, such as a machine, prime mover, or motor I43. Similarly, a three-phase alternating current generator I45 is driven by a rotating device, such as a machine, prime mover or motor I41. Phases A, B and C of the generator I4| respectively correspond to phases A, B and C of the generator I45. Phases A, B and C of the generator I4| are connected through a measuring device I49 (shown in broken lines) to the phases A, B and C of the generator I45. The measuring device I49 comprises electrical measuring instruments I5I, I53 and 55, each of which may employ a bridge circuit as shown in Fig. 3 and a DArsonval type of electrical measuring instrument as shown in Fig. 2.

The electrical measuring instrument I5I has its terminals connected between phases A and A of the generators MI and I45. The electrical measuring instrument I53 has its terminals connected between phases C and B of the generators MI and I45, and the electrical measuring instrument I55 has its terminals connected between phases B and C of generators MI and As pointed out with reference to Figure 1, one electrical measuring instrument, instrument I5I, is connected between corresponding phases of the two generators or systems, and the remaining two electrical instruments, instruments I53 and I55, are connected between differing remaining phases of the two generators or systems.

To facilitate describing the cperation of Figure 1, it will be assumed that the voltages are alike in each phase of the three-phase systems I and 5. It will also be assumed that all the instruments rotate in a clockwise direction when an increase in voltage is applied to the terminals of the instruments.

In Figure 1 the circuit breaker 3 is to be closed to connect the systems I and 5 only when the two systems are in synchronism and the proper phase relationship exists between the two systems. With the two systems in synchronism and in phase, the indicator of the voltmeter II will remain at zero and the voltmeters I3 and I5 aeecgaooi will indicate a voltage which is the' of-"thevoltage between any phase and ground. With'aslight diiferencein frequencythe indicators or pointers 2!, 23 and 25 will outlinea triangular figure which will rotate and'shift about the face of the indicating device I. The direction in which the triangle rotates about the dial of theindicating device 1', indicateswhich systemhas the greater frequency.

As the systems gradually approach synchronism, the speed at which the triangle rotates gradually decreases. The indicators andthe triangle outlined, becomestationary whenthe twosystems are in synchronism. Although-the two systems are in synchronism, the twosystems are out of phase until the indicator .2I of instrument I! I is at its zero position. When indicator 2| remains at the zero position, the circuit breaker 3 may be closed to connect systems land 5 together.

Referring to Fig. 4 it may be assumedthat the generators IM and 145 are identical and rotate in a clockwise direction, as indicated by the arrows.

Although the generators MI and I45 may have a direct-current field winding, it is believedpreferable to employ a three-phase; tachometertype of generator having a permanent-magnet field if the invention is to be employed on aircraft where simplicity, minimum weight and compactness are important.

With the use of a low-burden synchroscope of the type herein described, the small tachometertype of generator can be used therewith to supply the very small amount of electrical energy required. The electrical measuring instruments I5I, I53 and I55 are preferably arranged so that their pointers rotate on a common dial.

It may be assumed that Fig. 5 shows the face of the indicating device i 49 in Fig. 4. Pointers I6], I53 and I65 have a common faceor dial I59, and each has an axis of rotation which is equidistant from the axes of rotation of the other two pointers. The face or dial I59ha-s a suitable indicia or scale for each of the pointers I61, I63 and I65. It may also be assumed that pointer I5! is the indicator for instrument I 5| and that pointers I63 and I65 are pointers for instruments I53 and I55, respectively. When the pointers Ifil, I63 and I65 arrange themselves and remain in the positions shown in the first or top view of Fig, 5, the pointer IBI indicating zero voltage, the generators MI and I45 and the motors I43 and I45 are in synchronism and are in the same phase relationship. If the generators I4! and I45 are not in synchronism and the motors I43 and I4! associated therewith respectively, are operating at different speeds, the indicators of the instruments I5I, I53 and I55 will tend to oscillate at a rate which is the difference in speed between the two motors. As the motors approach synchronization, the speed of the oscillation will decrease and when the motors are rotating at the same speed the pointers will remain stationary. Although the two motors may be operating at the same speed and the generators may have the same frequency, the generators may not be in phase. The relative phase positions of the generators may be further adjusted so that the instrument I 5| continues to indicate a zero voltage.

The second or middle view of Fig. 5 shows the relative position of the indicators that is maintained when the generator I45 is lagging the generator MI by 120 or leading the gencrater-d4! ."by:1'240 The thirdion'bottom view: of Fig. 5 shows the relative position of the-point ers :that 'is. maintained when generator I45 is leading. generator MI. by or lagging-gen-. erator MI by 240.

It is to be observed that in each of the views in Fig. 5 a triangle is outlined by the pointers and, one-and only one pointer in each view is at the zero position. views shows one of the indicators at zero .position, it .is to be pointed thatin intermediate positions or other phase relationships, none-of the pointers indicate zero but the pointers neverthe-less continue to outline a. triangle.

If, for example, a pilot were to operate amultienginedairplane with a synchroscope as herein. descrihed'the synchroscope having a face or dial I59 with pointers arranged thereon as shown in Figure 5, the movement of the pointers andthe rotation of the triangle outlined thereby would attract his attention and indicate that the-engines were out of synchronism. If the triangle: outlined by the pointers rotates in a clockwise direction, the pilot immediately realizes that the engine or motor I43 is rotating faster than the engine or motor I41. By gradually decreasing the speed of motor I43, the rate at which the triangle outlined by the pointers rotates will decreaseand eventually the triangle will =become stationary. However, if the triangle outlinedby the pointers subsequently begins to rotate in a counter-clockwise direction, the 1101; realizes that he has decreased the speed of the motor-I43 to too great an extent. By adjusting the relative speeds of the .motors I43 and I45, the pilot 'canobserve the indicators on the dial I59 and know that the motors are in synchronization when there is no movement of the indicators. the generators MI and I45 are in synchronism and their phase relationships are such that the indicator I5] is at the center or zero position, the remaining (two indicators I63 and I65 with the Althoughthe invention has been described with reference to certain specific embodiments thereof numerous modifications are possible. Therefore, the appended claims have 'been drafted to cover not only the specific embodiments therein, but also all other embodiments falling within the spirit and scope of the invention.

I claim as my invention:

1. Apparatus for indicating the phase relationship between two, three-phase systems comprising three electrical measuring instruments with indicators, each electrical measuring instrument being connected between the two, three-phase systems, the first one of the electrical measuring instruments being responsive to a difference in voltage between corresponding phases of the two, three-phase system-s, a second one of the electrical measuring instruments being responsive to a difference in voltage between other differing phases of the two, threephase systems, and a third one of the electrical measuring instruments being responsive to a difference in voltage between difiering remaining phases of the two, three-phase systems, the indicators associated with the electrical measuring instruments traversing a common dial and overlapping to define a triangle when one or Although each of the three Whenv 7 more of the electrical measuring instruments is energized.

2. A synchroscope for connection between two three-phase electrical systems comprising in combination, three electrical measuring instruments with indicators associated therewith, said indicators traversing a common dial and outlining a triangle when one or more of said electrical measuring instruments is energized, the position of said triangle conveying information as to phase relationships between the two systems.

3. A synchroscope for connection between two three-phase electrical systems, having in combination two groups of terminals, each group comprising a first, second and third terminal for connection to the respective phases of one of the three-phase electrical systems and three electrical measuring instruments associated with a common dial, each electrical measuring instrument being connected between the two groups of terminals and having an indicator which retates in only one predetermined upscale direction about an axis when an electrical quantity is applied to said instrument, the first of said electrical measuring instruments being connected between the first terminals of the two groups, the second of said electrical measuring instruments being connected between the second terminal of one group and the third terminal of the other group and the third of said electrical measuring instruments being connected between the remaining terminals of the two groups, said three electrical measuring instruments being angularly positioned about a second axis parallel to the axes about which the indicators rotate, said indicators being of a length to extend beyond said second axis and being disposed to overlap above said dial when the instruments are deenergized, said indicators opera-ting to define a triangular pattern which is rotatable in a direction dependent upon the relative frequencies or" the systems.

4. A synchroscope for connection between two three-phase systems, having in combination two groups of terminals, each group comprising a first, second and third terminal for connection to the respective phases of one of the three-phase electrical systems and three electrical measuring instruments associated with a common dial, each electrical measuring instrument being connected between the two groups of terminals and having an indicator which rotates in only one predetermined upscale direction about an axis irrespective of the direction of the flow of current between the terminals to which the instrument is connected, the axes about which such indicators rotate, being substantially parallel to and equidistant from a second axis toward which the indicators are directed when the instruments are deenergized, said indicators being of a length to extend beyond said second axis and being disposed to overlap one another above said dial when the instruments are deenergized, the first of said electrical measuring instruments being connected between the first terminals of the two groups, the second of said electrical measuring instruments being connected between the second terminal of one group and the third terminal of the other group and the third of said electrical measuring instruments being connected between the remaining terminals of the two groups, said indicators cooperating to form a triangular pattern which is rotatable in a direction dependent upon the relative frequencies of the systems, and said indicators also cooperating when said systems are in synchronism to indicate by their relative positions the phase relation of said electrical systems.

HERBERT T. RIG-HTS.

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